Role of a class DHC1b dynein in retrograde transport of IFT motors and IFTraft particles along cilia, but not dendrites, in chemosensory neurons of living Caenorhabditis elegans

The heterotrimeric motor protein, kinesin-II, and its presumptive cargo. ca n be observed moving anterogradely at 0.7 mu m/s by intraflagellar transpor t (IF-T) within sensory cilia of chemosensory neurons of living Caenorhabdi tis elegans! using a fluorescence microscope-based transport assay (Orozco, J.T., K.P. Wedaman, D. Signor, H. Brown, L. Rose, and J.M. Scholey. 1999. Nature. 398:674). Here, we report that kinesin-II, and two of its presumpti ve cargo molecules, OSM-1 and OSM-6, all move at similar to 1.1 mu m/s in t he retrograde direction along cilia and dendrites, which is consistent with the hypothesis that these proteins are retrieved from the distal endings o f the cilia by a retrograde transport pathway that moves them along cilia a nd then dendrites, back to the neuronal cell body. To test the hypothesis t hat the minus end-directed microtubule motor protein, cytoplasmic dynein, d rives this retrograde transport pathway, we visualized movement of kinesin- II and its cargo along dendrites and cilia in a che-3 cytoplasmic dynein mu tant background, and observed an inhibition of retrograde transport in cili a but not in dendrites. In contrast, anterograde IFT proceeds normally in c he-3 mutants. Thus, we propose that the class DHC1b cytoplasmic dynein, CHE -3, is specifically responsible for the retrograde transport of the anterog rade motor, kinesin-II, and its cargo within sensory cilia, but not within dendrites.